Discharge-tube system



March 11, 1930. w HAHNEMANN 1,750,102

DISCHARGE TUBE SYSTEM Filed June 21, 1928 IHVENTOR U/a/Ter' H /mema n n ATTORNEY Patented Mar. 11, 1930 {UNITED STATES PATENT-l OFFICE WALTER HAHNEMANN, F BERLIN-MARIENFELDE, GERMANY, ASSIG'NOR TO C. LO- BENZ AKTIENGESELLSCHAFT, OF BERLIN-TEMPELHOIE, GERMANY DISCHARGE-TUBE SYSTEM App1ication filed June -21, 1928, Serial No. 287,274, and in Germany June 24, 1927.

This invention relates to electric devices producing what is called a negative characteristic, i. e., which produce an increasing terminal Voltage with decreasing current flow- 5 ing through it and vice versa. Such devices have been used in high frequency engineering for different purposes such as for generators of high frequency oscillations, amplifiers, and the like.

The object of the present invention is to provide means for improving the stability and reliability of electric devices using a neg ative resistance characteristic.

Another object of the invention is to provide a system of operation of an electric discharge device with a negative resistance characteristic, which provides a great stability, thus complying with the requirement of reliability for practical operation.

In a preferred specific embodiment the invention has been illustrated by the accompanying drawing showing an electric discharge device together with the necessary connections for carrying the invention into practice. The following detailed description taken with reference to the drawing will make the subject matter of the invention clearer and is intended to bring out its broad principle as contained in the appended claims.

High frequency devices for production of electric oscillations are known making use of a so-called negative resistance. By such a device is understood, as is well known, one

producing a decreasing terminal voltage with increasing current flowing through it, such,

e. g., as is the case with an electric arc. An.

oscillatory electric circuit connected to the terminals of such a device in a suitable manner will maintain electrical oscillations, the

frequency of which is determined by the natural frequency of the oscillatory circuit and to a more or less degree by the value of the negative resistance or the slope of the resistance characteristic. In case the negative resistance is not large enough to overcome the positive resistance of the circuit, i. e., its losses and oscillations will not be maintained, the negative resistance device may serve to effeet amplification of currents applied to it and may be used in connectionwith a receiving circuit.

When using electric discharge devices such as vacuum tubes having a number of electrodes, a negative resistance effect between two electrodes may be obtained by applying suitable voltages to further auxiliary electrodes or by the provision of electric or mag netic fields influencing the beam of discharge current. Such a tube has, e. g., become known under the name of dynatron which comprises a heated electrode, an anode and an auxiliary anode placed between the cathode and the anode. By applying to the main anode and the auxiliary anode a suitable positive potential the production of secondary electrons at the anode is caused; these are traveling against the main electron stream emitted by the cathode, whereby a negative resistance eifect between the two anodes is produced.

Another discharge tube of this type is described in the prior U. S. application Serial No. 568,551 and is represented schematically in the accompanying drawing. This tube has an ordinary electron-emitting cathode and an anode between which the negative resistance characteristic is to be produced. For this purpose the discharge electron stream passing from the incandescent cathode to the anode is deflected from its main path by two forces acting in opposition to each other. At a certain anode voltage both forces are just equally opposed and for other voltages they vary according to different laws as functions of the anode voltage whereby the resultant deflection produces a negative resistance efiect.

Let it be supposed that the value of the negative resistance is 1" which may be represented by the tangent of the curve representing terminal voltage as a function of current, i. e., a falling voltage-current characteristic. Furthermore the oscillatory circuit connected with the negative resistance path is assumed to have a self-inductance L, capacity C and an ohmic resistance to which is constituted by the loss resistance and the load resistance. As a result of a theoretical analysis it is found that the frequency (f) of the oscillations 100 produced in the circuit is given by the folowing formula In practical cases the factor l/CL predominates over the factor The condition when the production of oscillation is possible is that: LO/L; 1/0 1 Within this range the frequency is not only dependent on the natural constants of the oscillatory circuit but also on the value of the negative resistance. This latter is subject to variations owing to variations of the heat ing current, the anode voltage or changes of the further factors determining the negative resistance. This again produces, as may be seen from the above formula corresponding variations of frequency.

According to this invention these frequency variations due to variations of the negative resistance are avoided or at least minimized. to a sufficient degree. For this purpose, the variation of a factor determining the negative resistance characteristic is compensated by a means responsive to variations of the resistance and adapted to counteract these variations.

Referring to the drawing, item 1 is an evacuated vessel having an incandescent cathode 3, and an anode 2; item 9 is a heating battery for the cathode and 11 is an anode battery. The stream of electrons emitted from the cathode 3 is passing to the anode 2 and is deflected from its path by an electric field produced by an electrode 4 connected to a voltage of an auxiliary battery 5. Moreover, there is a magnetic field produced by a coil 7 energized by a battery 6, which field is disposed perpendicularly to the electron stream; this field acts on the electron stream in combination with the electric field in such a Way that the voltage between cathode S and anode 2 is decreasing when the current through the tube increases.

According to this invention there are provided coils 8 and 10 for producing additional magnetic field; these coils are energized by the heating current of the cathode and the voltage of the anode battery respectively; item 12 is the capacity and 13 is the self-inductance of the oscillatory circuit placed in parallel relationship between cathode 3 and anode 2, i. e., the path of the negative resistance. Thus oscillations of a frequency as stated above will be maintained in the circuit 12, 13 without the use of any reaction of this circuit on a controlling circuit as is the case with the well-known vacuum tube feed back generator. If in a system as represented by the drawing the heating current changes due to some cause, this would result in a change of the intensity of the electron stream, i. e., a change of the negative resistance r as may be seen from the theory given above. The heating current, however, produces an additional magnetic field by virtue of the coil 8 whereby another change of the negative resistance is effected. Both coils 7 and 8 are so wound and are given such a number of turns with respect to each other that the changes of the negative resistance caused by the change in the heating current is compensated by the change caused by the current in the winding 8. Thus, the negative resistance maintains its value and a variation of the frequency of the oscillations is avoided. The same holds true for variations of the anode voltage, the influences of which on the value of the negative resistance are compensated by the auxiliary field of the coil 10. Condensers 14 and 15 are placed parallel to the windings of the coils 8 and 10 respectively in order to prevent the high frequency currents in a the circuit 12, 13 from passing through the coils 8 and 10 respectively. In this manner any means determining the value of the negative resistance and responsive to any other factor determining the value of the negative resistance may be employed for compensating the variations, due to this factor.

Having described my invention, What I believe to be new and desire to secure and protect by Letters Patent of the United States 1s: 1. Means for maintaining constant the negative resistance characteristic of electric devices comprising means determining the value of said negative resistance and further means dependent on variations of said resistance for controlling said first mentioned means to influence said resistance in such a way as to compensate said variations.

2. In an electric discharge device having main electrodes, means to produce an electric discharge stream between said electrodes, means acting on said discharge stream to produce a negative resistance effect between said main electrodes and means responsive to said first means and adapted to influence the value of the negative resistance in such a way as to compensate variations of the negative resistance caused by variations of said first means.

3. In an electron discharge device having an incandescent cathode and anode, means to produce an electric field and means to produce a magnetic field, both fields acting on the electric discharge stream passing from the said cathode to the anode in such a way as to produce a negative resistance effect be tween said cathode and anode, additional magnetic fields responsive to variations of factors determining the value of said negative resistance and adapted to influence said reice ios

- sistance in such a way as to compensate said variations.

4. In an electron discharge device having an incandescent cathode and anode, a heating current source for said cathode, a source of high tension voltage for said anode, means to produce an electric field and means to produce a magnetic field, both fields acting on the electric discharge stream passing from said cathode to said anode in such a Way as to produce a negative resistance efiect between said cathode and said anode, additional magnetic fields responsive to variations of said heating current and said anode voltage respectively and adapted to influence said resistance in such a way as to compensate said variations.

5.In an electric discharge device having main cathode and anode electrodes between which a stream of electrons may pass, a heating current source for said cathode, a source of high tension voltage for said anode, means for producing adjacent the path of electrons a constant electro-static field to deflect the electron stream, means for producing adjacent the path of electrons a constant electromagnetic field adapted to equally oppose the deflection of the electron stream by said electrostatic field at a certain potential on the anode and to unequally oppose the deflection of the electron stream at higher potentials on the anode so as to deflect the electron stream, thereby decreasing the number of electrons that reach the anode, thus producing the desired negative resistance characteristic between said cathode and said anode, magnet coils energized by said heating current source and the anode voltage source respectively and producing additional magnetic fields for said main electric field in such a way as to compensate variations of the negative resistance characteristic caused by variations of said heating currents and said anode voltage respectively.

6. In an electron discharge device having an incandescent cathode and anode, a source of high tension voltage for said anode, means to produce an electric field and means to produce a magnetic field, both fields acting on the electric discharge stream passing from said cathode to said anode in such a way as to produce a negative resistance eflect between said cathode and said anode, and an additional magnetic field responsive to variations of said anode voltage and adapted to influence said resistance in such a way as to compensate said variations.

7. In an electron discharge device having an incandescent cathode and anode, a heating current source for said cathode, means to produce an electric field and means to produce a magnetic field, both fields acting on the electric discharge stream passing from said cathode to said anode in such a way as to produce a negative resistance eflect between said cathode and said anode, and an additional magnetic field responsive to variations of said heating current and adapted to influence said resistance in such a way as to compensate said variations.

In testimony whereof I have affixed my signature.

WALTER HAHNEMANN. 

